Photophysical and nonlinear absorptive optical limiting properties of [60]fullerene dimer and poly[60]fullerene polymer

A systematic study of the photophysical properties and nonlinear absorptive optical limiting responses of the [60]fullerene dimer (C(60) dimer) and poly[60]fullerene (poly-C(60)) polymer in room-temperature solutions is reported. The results are compared with those of C(60) and representative C(60) derivatives. While the absorption, fluorescence (spectrum, quantum yield, lifetime), and photoinduced electron-transfer properties of the C(60) dimer are somewhat different from those of C(60), they are qualitatively similar to those of other C(60) derivatives. The triplet-triplet absorption of the C(60) dimer is noticeably weaker than those of C(60) and other C(60) derivatives, corresponding to lower optical limiting responses of the C(60) dimer at 532 rm. However, the photophysical and nonlinear absorptive optical limiting properties of the poly-C(60) polymer are significantly different. The polymer solution shows much weaker fluorescence, barely detectable tripler-state absorption, and marginal optical limiting response. The different excited-state and nonlinear optical properties of the poly-C(60) polymer are explained in terms of new excited singlet-state decay pathways in the polymer that are not available in monomeric and dimeric C(60) molecules. In addition, the issue concerning significant excited-state fullerene cage-cage interactions in the C(60) dimer and poly-C(60) polymer is discussed.